Gutta percha and gutta percha-like natural and synthetic rubbers and thermoplastics do not adhere well to posts and obturators. Many posts and obturators are made of glass fiber-reinforced dental resins and their components are dissimilar to gutta percha and other thermoplastics that are molded onto the appliance. The surface wettability of the post and obturator are low due to at least two reasons: a) the matrix resins used to make the fiber-reinforced composite of the post and obturator are of a hydrophobic rather than hydrophilic nature; and b) the surface is precured leaving an insufficient number of unsaturated chemical bonding for further reaction. Both of these factors will work against good adhesion between the post or obturator and the gutta percha or other hydrophobic thermoplastic or other material.
Similar bonding problems exist between dental substructure materials and overlayer veneer materials. The general practice is to partially light cure the fiber-reinforced composite substructure and to keep an oxygen-inhibited layer for better wetting of the subsequent overlayer materials. However, the oxygen-inhibited layer itself is expected to be weak in strength and consequently poor adhesion along this layer is likely. To eliminate this weak layer, a higher degree of conversion in the absence of oxygen is required. This practice, however, limits the availability of unsaturated bonds on the surface for any future adhesive procedures.
The application of additional layers of material to an understructure has been taught in the art whereby plasma deposition is used to apply the layers to the understructure. U.S. Pat. No. 5,873,725 is directed to a dental post having a layer of ceramic material deposited over and bonded to the outside surface to facilitate adhesion of the post to a dental adhesive. The surface of the post is first roughened to increase the surface area of the post and thereafter a layer of ceramic material is applied by sputtering or plasma spray deposition. The layer of ceramic material does not alter the surface of the post, but adds an additional layer of material, namely ceramic, to the post. Similarly, U.S. Pat. No. 5,480,301 is directed to an orthodontic appliance whereon particles of stainless steel, ceramic, ceramic-metal composite, or metal-metal composite materials are applied to the surface of the orthodontic appliance by plasma spray coating, arc spray coating, flame spray coating or vacuum sputtering.
It has also been known to use plasma deposition for enhancing the bond strength of fibers to the matrix material in a fiber reinforced composite material. Commonly owned U.S. Pat. No. 6,200,136 is directed to a fiber-reinforced dental bridge material wherein the material comprises fibers embedded in a polymeric base material. In order to enhance the bond between the reinforcing fibers and the base material, thereby enhancing the reinforcing effect, the patent teaches silanizing or otherwise treating the fibers by etching, chemically grafting, plasma treating, or ion-bombarding. U.S. Pat. No. 5,829,979 is directed to a reinforcing material for dental appliances and prostheses. The reinforcing material is sometimes pretreated with a cold gas plasma or other such process that will increase the wetability and chemical activity of the material and thereby enhance the ability of the material and the resin to adhere.
The aforementioned prior art has been limited to bonding processes used during the impregnation of fibers in a polymeric matrix or to the actual addition of layers to an understructure.
Attempts have been made to improve the bonding between posts and obturators and gutta percha by applying silane or a silane/resin mixture to the post and obturator. Nevertheless, the bond is still quite weak.
It is desirable to increase the bond strength between posts and obturators and gutta percha or gutta percha-like natural or synthetic rubbers and thermoplastics. It would be beneficial to improve the bond strength between dental substructures and composite veneering materials.